The research plan, proposed as a collaborative effort between The Wistar Institute and the University of California, San Diego, will explore somatic cell hybridization for mapping genes on chromosomes. Interspecies hybridization with human cells will be the major focus of this research. This will permit a systematic approach to the assignment of genes for enzymatic phenotypic markers to specific chromosomes; exploratory work indicated the feasibility of this approach in regard to the gene regulating the enzyme, hypoxanthine guanine phosphoribosyl transferase. The identification of the human regulatory gene for hormonal induction of tyrosine amino transferase opens new avenues to the understanding of the mechanism of somatic cell regulation. The use of X-autosomal translocations in the studies will also be emphasized. Another major objective of this research will be to develop new methods that reliably separate human proteins from those of other species.